Control/Expansion Joints - How Deep, How Soon?

[Bobbyd38]

Poured new Floor today 24' x 48', 4" deep 3500# mix.

My Contractor wanted to come back in a few days, but I've heard different… How long before he should cut, and what is the recommended Depth?

Thanks,
Bob

 

[nehog]

http://construction.about.com/od/Concrete/a/Saw-Cuts-In-Concrete.htm

 

[Reflex]

Bobby,

I noticed that you didn't say where you are or the conditions in which your slab was poured or is curing (inside/outside/temp/humidity).

As a general rule, you want to get the expansion joints cut as soon as possible. When the slab cures it shrinks, that's what causes the first cracks. Concrete cures significantly within the first 24-36 hours. I noticed you posted at 6:00 last night, I'd be on that slab today (depending on conditions). Granted you don't want the slab to be too green, but I'd say 30 hours (depending on conditions) would be a good rule of thumb. If you wait to long, it's going to make it's own expansion joints.

Remember, the slab IS going to crack, expansion joints just tell it where. Most people don't realize that there are cracks at the bottom of their expansion joints.

Regarding depth, it depends. Rule of thumb for basic 4"-6" would be 1/3 depth.

I'm sure there are more opinions here, but that's how I do it.

Good luck!

 

[JACDes]

1/4 the slab depth or 1" for a 4" slab.
1 1/2" for 6
2" for 8
etc.

Saw cut control joints should be done within 24-72 hours (1-3 days) after the slab is poured.

 

[Firebird 1]

we have "control joints" cut before the finisher leaves the job with a softcut saw. "expansion joints" are installed before the pour. They can be done in a number of ways, asphalt, foam, wood, plastic, etc.